This invention relates to a slotting milling cutter, more specifically to an improved slotting milling cutter typified, for example, by a finger joint cutter for cutting a plurality of fingers at end portions of wood planks.
Finger joint is widely put in practical uses as means for joining a plurality of wood planks at their ends. The finger joint refers to a technique of forming a plurality of mountain range portions 12 at an end portion of each wood plank 10 as shown in FIG. 15, and then opposing the mountain range portions 12 of one wood plank 10 to those of another wood plank 10, followed by compression of these two wood planks 10 against each other to achieve fitting engagement, as shown in FIG. 16. These mountain range portions 12 are called fingers because of their shapes, and a slotting milling cutter for forming such fingers is generally referred to as a finger joint cutter. Incidentally, a suitable adhesive is applied to the mountain range portions 12 of wood planks 10 before they are fitted to each other.
Generally, a finger joint cutter essentially consists of a cutter body to be inserted and fixed to a spindle of a finger cutting machine and a plurality of projected cutting blades arranged at intervals, for example, with a center angle of 90xc2x0 on the circumference of the cutter body to protrude radially outward. The pluralities of projected cutting blades are arranged in the axial direction of the cutter body in a comb shape. Each projected cutting blade is composed of a pair of tapered faces. The projected cutting blades assuming a comb shape are designed to have a profile as a whole such that they can cut a fingered portion (mountain range portions) 12 as shown in FIG. 15.
While the finger joint cutter described above is of the type where the projected cutting blades are fixed integrally to the cutter body, there is also practiced a blade replaceable type having projected cutting blades attached removably thereto. FIG. 11 shows such blade replaceable type finger joint cutter, in which blade bodies 22 are arranged on the circumference of a cutter body 20 at predetermined pitches (at equal pitches or unequal pitches) and are removably fixed by bolts 23 respectively. Each blade body 22 has a plurality of projected cutting blades 24 formed in a comb shape parallel to the thickness, as shown in FIG. 12. That is, in the blade replaceable type finger joint cutter, the blade bodies 22 having projected cutting blades 24 each formed in a comb shape are designed to be detached from the cutter body 20 for replacement. The replaceable blades include right-side blade bodies 22 and left-side blade bodies 22 which are used separately depending on the kind of finger joint cutter. Provided that the pitch between tips of two adjacent fingers in the fingered portion 12 (see FIG. 15) is p, projected cutting blades 24 are formed at pitches 2p in a right-side blade body 22. While projected cutting blades 24 are also formed at pitches 2p in a left-side blade body 22, the blades 24 in the left-side blade body 22 are shifted by 1p leftward parallel to the thickness of the cutter body 20 with respect to the right-side blade body 22. Right-side blade bodies 22 and left-side blade bodies 22 are arranged alternately on the circumference of the cutter body 20. However, in the finger joint cutters shown in FIGS. 11 and 12, the right-side blade bodies 22 and the left-side blade bodies 22 are of the same configuration, and the left-side blade bodies 22 are positioned on the circumference of the cutter body 20 to be shifted leftward by 1p (1 pitch) thicknesswise with respect to the right-side blade bodies 22. In other words the blade bodies 22 shown in FIGS. 11 and 12 serve both as left-side blade bodies and right-side blade bodies.
The present invention relates to a blade body structure for forming an excellent film by physical vapor deposition (PVD) on a blade body 22 in a finger joint cutter. First, problems inherent in the prior art and special terms frequently appear in detailed description of the invention will be described. FIG. 13 is a perspective view of the blade body 22 viewed against the rotational direction thereof, and FIG. 14 is a perspective view of the blade body 22 viewed in the rotational direction thereof. In FIG. 13, the reference number 26 denotes a cutting edge in a projected cutting blade 24, and the reference number 28 denotes a rake face in the blade body 22. Side faces of the projected cutting blades 24 excluding the cutting edges 26 and the rake faces 28 are referred to as side flanks 30. Bottom edges 32 are formed at troughs present between one projected cutting blade 24 to be on the same plane as the rake faces 28 of the projected cutting blades 24 are formed. Further, slant bottom faces located at troughs of projected cutting blades 24 and formed contiguous to side flanks 30 of each opposing pair of cutting blades are referred to as major flanks 34. It should be noted here that there are cases where the bottom edges 32 have no sharp cutting edges. For example, when end faces of finger tips are to be formed using a finger joint cutter, the bottom edges need cutting edges. However, cutting edges are not necessary in the bottom edges when end faces of wood planks are cut beforehand using a circular saw to form finger tip end faces without cutting end faces of the finger tips using the finger joint cutter.
While blade bodies 22 of finger joint cutters are generally made of a hard material such as a high speed tool steel and a cemented carbide, there is supposed those having steel materials as bases to which such hard materials are joined. A technique is recently put into practice in order to increase durability of cutting edges in projected cutting blades 24. According to this technique, a hard film such as of titanium (Ti) compound and chromium (Cr) compound is formed by physical vapor deposition (PVD) on the flanks along the cutting edges. However, a blade body 22 having a complicated configuration with a plurality of projected cutting blades 24 in a comb shape as shown in FIG. 12 involves a problem in that it is difficult to form an excellent film uniformly by means of PVD. That is, in FIGS. 13 and 14, films to be formed on the side flanks 30 located between every opposing two projected cutting blades 24 and on the major flanks 34 around intersections of the side flanks 30 with the major flanks 34 of the bottom edges are porous or very thin and have extremely low adhesion. This is because excellent films are formed on the tips of the projected cutting blades 24 to make ions to be deposited hard to run through the clearances between the projected cutting blades to reach to the vicinities of the intersections.
While the rake faces 28 of the blade body 22 are sharpened in order to sharpen the cutting edges 26, there is pointed out a problem that the films come off during this treatment at such portions having films formed thereon with poor adhesion as described above. Even if a fingered portion 12 as shown in FIG. 15 is machined with a finger joint cutter to which blade bodies 22 having such durable films with poor adhesion are attached, the blade bodies 22 do not show sufficient durability, and the cutting edges 26 near the trough of the blade bodies 22 or those of the bottom edges 32 are dulled soon. The portions near the troughs of the projected cutting blades 24 perform machining of portions around the tips on the tapered faces of the fingered portion 12, and if such portions come to have poor cutting performance, the finger tips of the fingered portion 12 come to have finished thickness greater than a design specification, as shown in FIG. 17. Such fingered portions 12 having inaccurate tapered faces involve a significant problem in that, when they are engaged with each other, as shown in FIG. 18, the finger tips of the fingered portion 12 fail to reach the troughs of the counter part, and that the tapered faces cannot be brought into intimate contact with one another to cause reduction in the jointing strength. In this case, adhesion of the films formed on the portions which participate in machining by the cutting edges 26 can be improved somewhat by forming deeper troughs. However, it gives rise to a problem that the strength of the projected cutting blades 24 is lowered, since projection of the projected cutting blades 24 having originally a small thickness is increased.
The present invention is proposed in order to solve the problems inherent in the prior art as described above, and it is an objective of the present invention to provide a blade structure in which excellent durable films can be formed by means of physical vapor deposition (PVD) on the side flanks of the projected cutting blades near the troughs thereof or on the major flanks of the bottom edges without sacrificing the strength of the blades.
In order to overcome the problems described above and to attain successfully the intended objective, the slotting milling cutter according to one aspect of the present invention contains blade bodies attached to a cutter body at predetermined pitches in the circumferential direction thereof, the blade bodies each having a plurality of projected cutting blades arranged in a comb shape, and bottom edges formed at troughs between the projected cutting blade and another projected cutting blade adjacent thereto on the same plane as rake faces of the projected cutting blades are formed; characterized in that bottom grooves having a width of 90 to 100% of that of the bottom edges are defined by cutting off the bottom edges, and then the blade bodies are coated with hard films. In this case, the bottom grooves having a width of 90 to 100% of that of the bottom edge are defined preferably from the rake faces in the bottom edges toward major flanks of the bottom edges respectively.
Meanwhile, in order to overcome also the problems described above and to attain successfully the intended objective, the slotting milling cutter according to another aspect of the present invention contains blade bodies attached to a cutter body at predetermined pitches in the circumferential direction thereof, the blade bodies each having a plurality of projected cutting blades arranged in a comb shape, and bottom edges formed at troughs between the projected cutting blade and another projected cutting blade adjacent thereto on the same plane as rake faces of the projected cutting blades are formed; characterized in that bottom grooves having a width of 70 to 100% of that of the bottom edge are defined by cutting off the bottom edges with an attack angle of 0xc2x0 to 105xc2x0, and then the blade bodies are coated with hard films. In this case, the bottom grooves having a width of 70 to 100% of that of the bottom edges are defined preferably from the rake faces in the bottom edges toward major flanks thereof, respectively. It should be noted here that the attack angle referred to herein means the angle formed by the slant face of the bottom groove with respect to the rake face.